This invention relates to radiant tube heaters used for radiant heating and heater assemblies adapted for use with radiant tubes.
In some heating applications, such as high bay or high ceiling applications or outdoor applications, forced air heating is relatively impractical due to the fact that warm convective air rises leaving lower areas or regions where people are located relatively cold. In these other applications where such common air heating systems are not practical, it is known to use heaters which generate radiant energy, this energy being transmitted to objects such as floors, tools and machinery. The heated objects can store the warmth and re-radiate it to surrounding air. In this manner, radiant heating can provide warm, comfortable conditions where people are congregated and the use of such heating can avoid wasting convective heat and can lower energy costs.
One known type of radiant heater is a radiant tube heater which employs a relatively long, radiant tube made of a suitable metal, this tube surrounding and enclosing an elongate flame projected from a burner head. This heater includes a combustion air blower which can be of standard construction, a burner nozzle connected to a combustible gas supply, and the burner head connected to the nozzle. The nozzle and head form a burner assembly which is positioned in a combustion air duct section forming a passage for combustion air. The outlet end of the blower is attached to an inlet end of the air duct section so that the blower is able to direct combustion air through the air duct section which can include a perforated equalizer plate so that air flow is approximately evenly distributed across the width of the air duct section before the combustion air reaches the burner assembly. The burner head, which is arranged centrally in the air duct section, creates an annular passageway between itself and the air duct section. The burner head has a substantially cylindrical inlet portion of relatively small diameter, a substantially cylindrical outlet portion having a diameter substantially larger than the inlet portion and a frustoconical intermediate portion extending between the inlet portion and the outlet portion and through which combustion air can flow into the outlet portion. The combustible gas, which can be natural gas or LPG fuel, is delivered to the heater through a gas valve governor to the burner nozzle which is installed in the upstream end of the inlet portion. Combustion air enters through vents or ports in the side wall of the inlet portion to intermingle or mix with the fuel, thereby producing a gas/air mixture that exits through a perforated ceramic tile mounted in the downstream end of the outlet portion. The exiting mixture is ignited by an electrode resulting in a long laminar flame extending down the radiant tube, this flame being up to sixteen feet in length or more. An end of the cylindrical radiant tube is secured to and extends from the downstream end of the air duct section and is heated by the long flame to emit infrared radiant heat. Typically, the radiant tube is located in the top portion of a downwardly-opening, trough-shaped reflector/shield. The reflector or shield in use receives upwardly-directed radiant energy from the tube and reflects or re-radiates this energy downwardly to a desired location for heating purposes. This known heater is relatively quiet and reliable in operation and relatively inexpensive to manufacture. However, there is a desire to provide radiant tube heaters which are more efficient, particularly in view of the relatively high cost of heating gas.
One form of radiant tube heater is described and illustrated in U.S. Pat. No. 5,429,112 which issued Jul. 4, 1995 to M. Rozzi. This heater has a housing and a radiant tube mounted within the housing along with a modular control box. The tube is made from aluminum coated steel such as that sold under the trade-mark “ALUMA-THERM”. A first open end of the tube is connected to an internal wall formed with a hole to receive the tube. The second open end of the tube protrudes from the housing and is for discharging the exhaust produced by the combustion of the gas and air mixture. The second end may be connected to an exhaust flue which vents the exhaust directly outside of a building. Mounted between the tube and the housing is a reflector which is made of an aluminum sheet buffed on its surface facing the tube. A burner is provided and mounted to the outside of this burner near its downstream end is an electronic ignition element in the form of a glo-bar electrically insulated from the burner.